Stars traditionally show up with close family members and significant others for the big honour, and Theroux took a front seat as his rumoured girlfriend posed for photographs and got down and dirty in the cement on a hot Hollywood morning.
Aniston, wearing a floral dress and nude heels, seemed to enjoy the big affair, and the attention of Theroux, who bent over with laughter as the actress first placed her hands in the cement.
She even blew him a kiss.
Pals Jason Bateman, who starred alongside Aniston in The Switch and new movie Horrible Bosses, and Chelsea Handler were also on hand to lend their support.
It's not the first time Theroux has joined Aniston at a major event - he recently sat in the front row for her taping of Inside The Actors Studio, for which Aniston was interviewed by host James Lipton for close to three hours.
The show will air in America on Monday (11Jul11).